Fruit peels are the primary by-product of the fruits industry accounting up to 30 % in some variants. The increased production of the fruits has to lead to an upsurge in the waste production. Hence, active research efforts are directed to the efficient use of the fruit peels to solve daily life and serious problems of mankind. Fruit peels of fruits such as apple, banana, and mango contain high amounts of minerals, viz., calcium, zinc, iron, manganese, etc.(Feumba Dibanda Romelle 2016).These minerals are essential for the well-being of people and may be procured to be used in other products. In this context, research on apple peels as a versatile biomass for water purification is already being conducted (Mallampati and Valiyaveettil 2013). Banana peels have proven to remove cadmium contamination (Memon, Memon et al. 2008). Fruit peels are used in formulating fertilizers (Mercy S 2014). Apart from these, the fruit skins also contain phenolic compounds in significant amounts which find uses in the food industry and the cosmetic industry.
This project focuses on analyzing the morphological, surface properties and compositions of the three specimens, comprising of peels of apple, banana, and mango. A detailed elemental analysis of the samples will lead to a broader picture of their probable applications. Further, investigating the morphology and surface properties of the samples will help in future surface modifications and alterations leading to efficient uses in industries.
Test and Analysis:
1. Critical point drying (CPD)
2. Sputter coating with gold
3. Optical Microscopy
4. Scanning Electron Microscopy (SEM)
5. EDS analysis
6. Electron Flight Simulation
7. Image Colorization
After peeling off the skins from apple, banana, and mango, they were cleaned thoroughly. Then the fruit peels were cut and sized to make them compatible for the microanalysis.
The fruit peels are biological samples. They were dehydrated before their placement in the vacuum chamber of the scanning electron microscope. Critical point drying (CPD) using ethanol and transitional fluid, liquid carbon dioxide, was employed for removing the water molecules from the samples. Further, to make the surfaces of the samples conductive gold atoms were sputtered on the top. Necessary sample preparation for sputter coating, including the use of carbon tape and carbon polish for grounding were carried out as practiced. Making the surface of the samples conductive and proper draining of the charge were important to inhibit charge accumulation and decorations on the samples.
Figure 1: The critical point drying (CPD)unit at the University of Rochester
Figure 2: The sputter coating unit at the University of Rochester
The samples were seen under optical microscopy primarily to locate areas of interest. This study was done before the dehydration processing of the samples. The data gave an idea about the structures present at the surface.
Figure 3: Optical microscopy images of peels of apple (top left), banana (top right) and mango (bottom)
Scanning Electron Microscopy:
The as prepared dehydrated and sputter coated samples were mounted for SEM analysis. Images were captured at different working conditions varying the accelerating voltage, working distance and magnification. Images were further recorded using various imaging modes. Particularly, backscattered electron imaging mode gave a preliminary idea on the composition of the sample. This information was a good starting for detailed elemental analysis of the samples.
Figure 4: SEM images of peels of apple (top), banana (bottom left) and mango (bottom right)
This technique coupled with the electron microscope made an elemental analysis of the samples. Quantitative information on the elements present in the sample were discerned using the available software. Further, care was taken to eliminate mislabeling of the peaks in the X-ray spectrum.
Figure 5: EDS analysis of peels of apple (top left), banana (top right) and mango (bottom)
Electron Flight Simulator:
The size and shape of the region of primary excitation was estimated by carrying out Monte Carlo simulations for organic sample.
Figure 6: Resulting electron flight simulator image of the sample
SEM images collected were colored using ImageJ software.
Figure 7: Colorized SEM images of the peels of apple (top left), banana (top right) and mango (bottom two)
Recycling of biological agro-waste is necessary to make better utilization of the available resources. Moreover, to implement any such process at a commercial scale studying the fundamentals of such material is essential. The work done in this project will help in a deeper understanding of the structural and morphological properties and compositions of the targeted agricultural by-products. Future investigation will be able to rely on the work done in this project.
I would like to thank Brian McIntyre for his constant support and encouragement throughout the coursework and project and my TA, Rakan, for helping me with the labs.
References and Further Reading:
Feumba Dibanda Romelle, A. R. P. a. R. S. M. (2016). "Chemical composition of some selected fruit peels." European Journal of Food Science and Technology
Mallampati, R. and S. Valiyaveettil (2013). "Apple peels--a versatile biomass for water purification?"ACS Appl Mater Interfaces
Memon, J. R., et al. (2008). "Characterization of banana peel by scanning electron microscopy and FT-IR spectroscopy and its use for cadmium removal." Colloids Surf B Biointerfaces
Mercy S, M. B. S., Jenifer I (2014). "Application Of Different Fruit Peels Formulations As A Natural Fertilizer For Plant Growth." International Journal of Scientific & Technology Research